The invention relates to an airbag for an airbag module of a motor vehicle.
Such an airbag may be filled with gas in order to protect an occupant of the vehicle in the event of a crash—by a sensor-controlled triggering of an associated gas generator. The airbag comprises a first airbag layer denoted as a lower airbag layer (the lower panel of the airbag, for example in the form of a fabric layer) and a second airbag layer denoted as an upper airbag layer (the upper panel of the airbag, for example in the form of a fabric layer) which are connected, for example sewn, to each other on their outer edges bearing against one another in order to form an airbag. When the airbag is installed for its intended purpose in an airbag module, the second airbag layer faces toward the occupant of the vehicle to be protected when inflated. The terms “lower airbag layer” and “upper airbag layer,” therefore, do not refer to “upper” or “lower” in a spatial sense but they refer to the arrangement of the respective airbag layer relative to the occupant of the vehicle to be protected.
Furthermore, an intermediate layer (an intermediate panel, for example in the form of a fabric layer) is arranged between the upper airbag layer and the lower airbag layer and which divides the interior of the gasbag, which is encompassed by the upper airbag layer and the lower airbag layer, into two chambers. The lower airbag layer is provided with a gas inlet aperture through which gas originating from a gas generator is able to enter the first chamber of the airbag defined by the lower airbag layer and the intermediate layer. An outlet means is provided in the intermediate layer through which gas from the first chamber of the airbag is able to enter the second chamber of the airbag which is encompassed by the upper airbag layer and the intermediate layer as well as parts of the lower airbag layer, so that according to the amount of gas introduced into the airbag through the inlet aperture, substantially only the first chamber or both chambers of the airbag are selectively filled with gas and thereby inflated.
The state in which substantially only the first chamber of the airbag is inflated, may be additionally differentiated from the state in which both chambers of the airbag are inflated, primarily by the internal pressure in the two chambers of the airbag. In the first-mentioned case whereon the first chamber is inflated, the internal pressure is many times higher in the first chamber of the airbag than in the second chamber of the airbag, into which gas flows, if required, to vent the first chamber of the airbag. Therefore, a pressure level only prevails in the first chamber of the airbag which is able to allow an effective protection of an occupant of the vehicle striking the airbag by energy reduction. In the second-mentioned case where both chambers are inflated, the pressure level in the two chambers of the fully inflated airbag is at least the same value; the difference between the two chambers should not be more than 50%. In contrast, in the first-mentioned case, the level of pressure in the first chamber regularly differs from the pressure in the second chamber by orders of magnitude.
For selectively inflating the airbag with a smaller amount or a larger amount of gas, therefore, a multi-stage gas generator, in particular a two-stage gas generator, may be used of which, depending on the size, the weight and/or the seating position of the occupant of the vehicle to be protected, either only the first stage or a plurality of stages (both) are triggered. Only the first stage of the gas generator is triggered when the occupant of the vehicle to be protected is a particularly small or a particularly lightweight person, for example a so-called 5% woman. In contrast, a plurality of stages of the gas generator are produced to produce a larger amount of gas if the occupant of the vehicle to be protected is a larger and/or heavier person, for example a so-called 50% man or 95% man. The size and/or the weight as well as the seating position of the respective occupant of the vehicle to be protected may, therefore, be detected by known sensors, for example positional or weight sensors. Depending on the position, in particular the seating position, of the occupant of the vehicle to be protected, variations of the aforementioned rule may be provided when triggering the gas generator. Thus, for protecting a particularly large occupant of the vehicle, it is possible for only one stage of the gas generator to be triggered and, accordingly, substantially only one chamber of the airbag to be inflated, when the occupant to be protected is positioned with the head or upper body particularly close to the corresponding airbag module. As a result, injuries to the occupant are designed to be avoided, by the airbag expanding when inflated. Such an arrangement is known from JP-A-09-188216.
An object of an embodiment of the present invention is to further improve an airbag for an airbag module of the aforementioned type.